Phosphodiesterase type 5 inhibitors as a treatment for erectile dysfunction: Current information and new horizons

Peer review under responsibility of Arab Association of Urology.

Figures & data

Figure 1 PDE5i promote penile smooth muscle cell relaxation and erection by preventing the degradation of cGMP.

Figure 2 The multifactorial causes of ED.

Figure 3 The molecular structures of clinically available PDE5i.

Table 1 Risk factors for ED.

Condition	Multivariate adjusted odds ratio
Antidepressant use	9.1
Antihypertensive use	4.0
Diabetes mellitus	2.9
Obstructive urinary symptoms	2.2
Current cigarette smoking	1.6
Hypertension	1.6
Benign prostatic enlargement	1.6
Obesity	1.5
Physical inactivity	1.5
Cardiovascular disease	1.1

Table 2 The selectivity of PDE5i for PDE isoforms, compared to PDE5 (PDE5 = 1). Larger values denote a lower binding affinity.

Isoform	PDE isoenzyme
	Sildenafil	Tadalafil	Vardenafil
PDE1	80	>4000	690
PDE2	>19,000	>4000	62,000
PDE3	4628	>4000	40,000
PDE4	2057	>4000	47,000
PDE6	11	188	35
PDE7	6100	>14,000	>300,000
PDE8	8500	>14,000	>300,000
PDE9	750	>14,000	5800
PDE10	2800	>14,000	30,000
PDE11	780	6	1620

Table 3 The common side-effects of PDE5i (>2% incidence).

Adverse event (%)	Sildenafil	Tadalafil	Vardenafil
Headache	16	15	15
Flushing	10	3	11
Nasal congestion	4	3	9
Dyspepsia	7	8	4
Abnormal vision	3	–	–
Sinusitis	–	–	3
‘Flu syndrome	–	–	3
Diarrhoea	3	–	–
Myalgia	–	3	–